# Multiline equation and text

I would really like to get a multiline equation with text explaining each step.

I've got close with

\begin{equation*}
\begin{split}
A \simeq & B  \mbox{[Lemma 8.35(iii)]} \\
\simeq & C \mbox{[exactness of first column - see Ex. 5.3]} \\
etc
\end{split}
\end{equation*} 


But I can't get tab spacing between the equation and the message box. Maybe an mbox is not the best way?

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The amsmath package offers a number of environments that can achieve what you want: here's an example (with annotations flushed right, and with annotations two quads appart from the equations):

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{align*}
A & \simeq B  \tag{[Lemma 8.35(iii)]} \\
& \simeq C  \tag{[exactness of first column - see Ex. 5.3]}
\end{align*}

\begin{alignat*}{2}
A &\simeq B   &\qquad & \text{[Lemma 8.35(iii)]} \\
&\simeq C   &\qquad & \text{[exactness of first column - see Ex. 5.3]}
\end{alignat*} 

\end{document}

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thanks for the help – Qwirk Mar 31 '11 at 1:51

You can also use intertext for short annotations of 1-2 lines.

\begin{align}
A_1&=N_0(\lambda;\Omega’)-\phi(\lambda;\Omega’),\\
A_2&=\phi(\lambda;\Omega’)-\phi(\lambda;\Omega),\\
\intertext{and}
A_3&=\mathcal{N}(\lambda;\omega).
\end{align}


see 3.10 Interrupting a display in amsmath

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amstex is, these days, mostly of historical interest. however, it was the basis for ams-latex, specifically amsmath, and the section 3.10 to which you refer is in the manual for amsmath. texdoc amsldoc` if you are working with a tex live system. – barbara beeton Dec 15 '12 at 20:49
Thank you... there is always enough time to make typos. ;-) – Jonas Stein Dec 15 '12 at 21:10